Luis A. Contreras

Integration of biomaterials implanted into abdominal wall: process of scar formation and macrophage response

The behaviour of two biomaterials polytetrafluoroethylene (PTFE) and polypropylene (PL) has been studied, focussing especially on the macrophage response to the implant, as well as on certain aspects of the process of scar formation. A total of 24 animals (white New Zealand rabbits) received prostheses implanted into the anterior abdominal wall in such a way as to involve every layer over an area of 7 cm x 5 cm. The interfaces formed with the visceral peritoneum, subcutaneous tissue layer and the recipient muscle-aponeurotic tissue were assessed. The techniques employed were light microscopy, scanning electron microscopy and immunohistochemical methods, the latter using a monoclonal antibody specific for rabbit macrophages (RAM-11). From the results obtained, it can be seen that: (a) the structure of PL allows its total integration with the reparative tissue, while PTFE becomes encapsulated, on both the subcutaneous and the peritoneal aspects, by orderly connective tissue; (b) the macrophage response, determined on the basis of the presence of labelled macrophages, shows a similar pattern in both biomaterials; and (c) angiogenesis is very intense in the PL mesh, whereas the PTFE prosthesis undergoes almost no vascular colonization.

Tissue response to polypropylene meshes used in the repair of abdominal wall defects.

The degree of integration of biomaterials used in the repair of abdominal wall defects seems to depend upon the structure of the prosthesis. Several polypropylene (PP) prostheses are currently available which differ in the number of PP filaments, the type of weave and the porosity. The aim of this study was to evaluate the integration, adhesion formation and resistance to traction of three types of PP prostheses (Marlex, Trelex and Prolene) used in the partial or total repair of abdominal wall defects. Abdominal wall defects (7 x 5 cm) were created in 54 New Zealand rabbits involving all the tissue layers (total substitutions (TS); n = 27) or all layers excluding the parietal peritoneum (partial substitutions (PS); n = 27). The defects were repaired with PP monofilament prostheses of different weave (1 mm porosity) (Marlex, n = 18; Trelex, n = 18) or bifilament (2 mm porosity) (Prolene; n = 18). They were placed in contact on one side with subcutaneous tissue and on the other with abdominal viscera or parietal peritoneum. Animals were killed at 30, 60 and 90 days and samples of prosthesis and scar tissue processed for light and scanning microscopy. The adhesion formation with viscera was evaluated. Resistance to traction was measured with a tensiometer using strips including the prosthesis and anchorage tissue. Adhesions were detected in all the TS and in four PS. Microscopic analysis revealed total integration of the TS samples by fibrous and disorganized tissue. Prostheses used for PS were integrated by white adipose tissue with the exception of the areas around the mesh nodes and anchorage zones. The foreign body reaction could be seen as a moderate accumulation of white blood cells. Tensiometric analysis showed an increase in resistance to traction with time (P < 0.001) in each type of prosthesis, but no differences were detected (P > 0.001) between them. We concluded that: (a) the formation of adhesions was almost inhibited when the parietal peritoneum was left intact; (b) in both TS and PS, polypropylene prostheses integrated completely although the composition of the scar tissue was seem to differ; and (c) resistance to traction was similar in both TS and PS.

Macrophage response to experimental implantation of polypropylene prostheses

We have assessed the macrophage response to polypropylene mesh (Marlex) implanted into the abdominal wall of New Zealand white rabbits, using RAM-11, a monoclonal antibody specific for rabbit macrophages. The response diminishes during the course of the first 90 days after implantation, although the presence of other cell types typical of foreign-body reactions increases. We have also confirmed the high degree of integration of the biomaterial into the wall achieved after 9 weeks. This has been determined using light and scanning electron microscopy. Likewise, we have observed the formation of numerous adhesions between the polypropylene mesh and the viscera of the abdominal cavity.

Neoperitoneal formation after implantation of various biomaterials for the repair of abdominal wall defects in rabbits

OBJECTIVE To study the interfaces between the visceral peritoneum and some of the biomaterials used to repair defects in the abdominal wall. DESIGN Animal study. SETTING School of medicine, Spain. MATERIAL 48 New Zealand white rabbits divided into 4 groups of 12 each. INTERVENTIONS Full thickness defects 50 x 70 mm were created in the abdominal wall and repaired with polytetrafluoroethylene (PTFE, Soft Tissue Patch), one of two polypropylene patches (Marlex and Prolene), or lyophylised dura mater (Lyo-Dura). 3 animals from each group were killed at 14, 30, 60 and 90 days and specimens examined by light microscopy, scanning electron microscopy, and immuno histochemistry by labelling of macrophages with RAM-11, a specific monoclonal antibody (MoAb). MAIN OUTCOME MEASURES Infection, healing, development of adhesions, and histological appearance of the interface. RESULTS Tissues responded similarly to materials of similar structures. Layered prostheses (PTFE and Lyo-Dura) caused formation of a well organised neoperitoneum with few adhesions to the abdominal viscera (loose adhesions in 2 animals in each group), whereas the mesh prostheses generated a disorganised neoperitoneum with many adhesions (Marlex loose adhesions 3, firm 8, and integrated 1; Prolene loose adhesions 2, firm 8, and integrated 2). Lyo-Dura was associated with the formation of areas of calcification. Labelling of macrophages with the MoAb showed that they were in direct contact with all materials studied. CONCLUSIONS Layered biomaterials with little or no porosity (PTFE and Lyo-Dura) are the most suitable of the four for implantation in sites where the prosthesis is in contact with the visceral peritoneum, because they induce minimal adhesions.

Similarity in behavior of polytetrafluoroethylene (ePTFE) prostheses implanted into different interfaces

The biomaterial ePTFE is widely used in the clinical environment for vascular replacement or bypass, as well as in the repair of tissue defects, especially those involving the abdominal wall. The objective of this study was to evaluate the healing response to ePTFE prostheses implanted into a circulatory interface and a tissue interface, each in a different animal species. For vascular implants, the Sprague-Dawley rat (n = 60) was used, while the New Zealand white rabbit (n = 20) was used in the tissue replacement model. In the former, a vascular microprosthesis measuring 5 mm in length and 1 mm in internal diameter, having a porosity of 30 microns, was implanted into the common iliac artery. In the rabbit, a 7 x 5-cm fragment of ePTFE (Soft-Tissue Patch) was implanted into a defect in anterior abdominal wall that involved all the tissue layers. In this case, the prosthesis was left touching the intestinal loops. The implants were studied between 14 and 90 days of postimplantation by means of light microscopy, scanning electron microscopy, and immunohistochemistry. The latter involved the use of anti-rat (MAC-341) and anti-rabbit (RAM-11) macrophage-specific monoclonal antibodies. The behavior of the ePTFE in the different interfaces (vascular and abdominal wall) was similar with respect to the following aspects: the prosthesis presented a process of encapsulation which was more intense on the outer surface; colonization of the implant was limited to the outermost two thirds, with minimal invasion of the middle portion; colonization was absent on the edges of the prosthesis; collagenization of the interstice of the mesh occurred late; the foreign body reaction taking place on the outer surface was similar in both interfaces, with formation of a barrier consisting of macrophages and giant cells that did not penetrate the prosthesis; and, finally, in neither of the two models was vascular colonization of the PTFE prosthesis observed; rather, the angiogenic process was limited to the periprosthetic zones. The integration of the implant made of ePTFE is similar despite the differences in interfaces and the use of different animal species. The macrophage response does not determine the success or failure of the implant.

Ultrastructural Alterations of Polytetrafluoroethylene Prostheses Implanted in Abdominal Wall Provoked by Infection: Clinical and Experimental Study

Abstract. Infection of an expanded polytetrafluoroethylene (ePTFE) prosthesis after implant is a major drawback of its use in current clinical practice. The aim of the present study was to compare the behavior of such prostheses implanted into New Zealand rabbits with that of prostheses infected after clinical implant. Experimental implants of ePTFE Soft Tissue Patch were performed to repair defects (7 × 5 cm) created in the abdominal wall of 10 rabbits. Prior to implant the prostheses were contaminated with Staphylococcus aureus. Five animals implanted with noncontaminated ePTFE prostheses served as controls. All the animals were sacrificed at 30 days after implant. For the clinical study, specimens were taken from three ePTFE implants that had been found to be infected after intervention. The clinical and experimental implant specimens were processed for light microscopy and scanning electron microscopy. Macroscopic and microscopic examination of experimental and clinical implants revealed alterations to the ePTFE structure, such as areas of fragmentation, fracture lines, and detachment of fine layers of ePTFE that harbored numerous Staphylococcus colonies. Neoformed tissue around contaminated implants was arranged more loosely, and on occasion large spaces between fibers gave rise to an “unknitted” appearance with respect to the control implants. It may be concluded that microporous ePTFE prostheses show similar behavior following experimental or clinical implant in the presence of infection. Irreversible changes to the structure of the prosthesis are produced owing to colonization of the biomaterial by microorganisms, which in most cases necessitates total replacement of the prosthesis.

Pathologic and Clinical Aspects of Repair of Large Incisional Hernias after Implant of a Polytetrafluoroethylene Prosthesis

Abstract. One of the alternatives for the repair of large incisional hernias is the use of a prosthetic material. The present retrospective study relates the experience acquired for treatment of large incisional hernias (hernial orifice > 10 cm) with ePTFE prostheses. Thirty-eight massive incisional hernias were repaired using ePTFE 1 mm thick Soft Tissue Patches. Twenty-four patients received a prosthetic patch of 10 × 15 cm, 13 a patch of 15 × 20 cm, and 1 a patch of 20 × 30 cm. In 30 cases the ePTFE was sutured to the recipient tissues with a double row of polypropylene stitches. For the first eight interventions the ePTFE was secured using a single row of polypropylene sutures. Pathologic studies of biopsies from patients who had undergone surgical reintervention at 40 days, 12 months, and 48 months, respectively, were done using light microscopy, scanning electron microscopy, and immunohistochemistry with human antimacrophage antibodies KP-1. The follow-up period for all patients was between 18 and 72 months. There was no perioperative mortality. No infection or rejection of prostheses was recorded. Seroma was present in four patients. Computed tomography was performed for evaluation purposes on 10 randomly selected patients (mean postoperative delay 1–4 years) and showed the ePTFE encapsulated by newly formed tissue. One of the patients suffered from mechanical intestinal obstruction 40 days after implant and suffered a recurrence a year later. Three recurrences at the patch–recipient tissue interface where the ePTFE had been secured with a single row of polypropylene stitches were recorded after 8, 12, and 28 months. At 40 days good integration of the biomaterial was observed in the newly formed tissue. On both sides of the implant an accumulation of four to six strata of cells was appreciable. Some of them were labeled with KP-1. Cell infiltration of the prosthesis was restricted to the most exterior third of the patch. There was no colonization at the patch–recipient tissue interface. At 12 and 28 months the cell barrier had almost disappeared. KP-1-labeled macrophages were scarce. Scanning electron microscopy revealed a well defined peritoneum. It may be concluded that: (1) a double suture row is recommended to secure the prosthesis; (2) ePTFE provides an adequate substrate for the formation of scar tissue; and (3) the macrophage response induced by the ePTFE decreases with time.

Use of nonporous polytetrafluoroethylene prosthesis in combination with polypropylene prosthetic abdominal wall implants in prevention of peritoneal adhesions

One of the drawbacks of using macroporous polypropylene prostheses in the repair of the abdominal wall is the formation of adhesions with the viscera. However, polytetrafluoroethylene (PTFE) has low adhesion formation, although it provides less resistance to traction in the repaired zone. The aim of the present study was to reduce the formation of adhesions to a polypropylene implant Prolene (PL) by introducing a nonporous expanded PTFE layer (Preclude Dura-Substitute) (PR) between the polypropylene prosthesis and the abdominal viscera. The scarring process and resistance to traction in the repaired zone were also evaluated. Thirty-six rabbits were divided into three groups and were treated as follows: group I, a PR patch (7 x 5 cm) was secured to the parietal peritoneum; group II, an abdominal wall defect (7 x 5 cm) was created and repaired using a PL patch; group III, an abdominal wall defect was as in group II and was repaired using a combined PR/PL prosthesis. Specimens were evaluated at 14, 30, 60, and 90 days postimplant for extent of adhesion formation and morphological analysis was performed using light and scanning electron microscopy. Biomechanical resistance of the implant was evaluated using strips comprising prosthetic material and anchorage tissue. Group I and group III prostheses showed loose adhesions only, but group II adhesions were firmly attached. The mean surface areas covered by adhesions were 0.08 cm2 (group I), 7.67 cm2 (group II), and 0.1 cm2 (group III). PR implants (group I) were encapsulated by organized tissue. In group II the formation of disorganized tissue invading the prosthesis was observed. In group III the PR impeded the growth of disorganized scar tissue and the lower surface of the implant was covered by an orderly neoperitoneum. Resistance to traction of the double implants (group III) (mean +/- SD, 33.32 +/- 0.9 N) was similar to that of the Prolene implants (group II) (33.76 +/- 0.46 N) (Mann-Whitney U test, p < 0.05). We concluded the presence of a PR layer between the PL implant and viscera greatly reduced the incidence of adhesion formation without affecting the high resistance to traction provided by the PL implant or the evolution of the scarring process.

Effect of phosphatidylcholine on the process of peritoneal adhesion following implantation of a polypropylene mesh prosthesis

The postimplantation peritoneal adhesions formed with some biomaterials continue to represent a serious problem when these biomaterials are placed in contact with the organs of the abdominal cavity. The objective was to test the effects of phosphatidylcholine (PC) in the attempt to modulate the adhesive process, thus improving the biomaterial/visceral peritoneum interface. We have carried out an experimental study using the New Zealand white rabbit, implanting a 7 x 5 cm2 polypropylene prosthesis into the anterior abdominal wall in such a way that it replaced all the tissue layers and was in contact with the intestinal loops. Three study groups were established: group I (control), in which only implantation of the biomaterial was performed; group II, in which the prosthesis was pretreated with a solution of PC; and group III, in which the implants were treated as in group II and the animals underwent intraperitoneal administration of 10 ml of the same solution. The animals were killed on postimplantation day 14. The total surface of the prosthesis occupied by adhesions was measured and light and scanning electron microscopy were performed to analyse the healing process. In comparison with the controls, groups II and III did not present significant differences with respect to the resistance or extension of the adhesions. The microscopic results showed a rapid formation of disorderly and well-vascularised scar tissue enveloping the entire prosthesis. Thus, PC was unable to modulate the process of adhesion formation between the prosthesis and the organs of the abdominal cavity; nor did it induce changes in the cells of sufficient importance to alter the results of the healing process in the presence of this biomaterial.

Experimental assay of a Dual Mesh® polytetrafluoroethylene prosthesis (non-porous on one side) in the repair of abdominal wall defects

The porosity of the prosthetic biomaterials used to repair defects in the abdominal wall seems to influence the tissue repair process insofar as tissue integration of the prosthetic material and the formation of adhesions with abdominal viscera are concerned. We studied the behaviour of a new type of polytetrafluoroethylene prosthesis used for the repair of abdominal wall defects. Dual Mesh (DM), which has two different faces; one face has a porosity between 30 and 60 microns, while the other is non-porous. In 20 New Zealand White rabbits, a full-thickness (except skin) 7 cm x 5 cm defect was created in the anterior abdominal wall that was repaired with DM. At 14, 30, 60 and 90 days, samples were obtained and studied by light and scanning electron microscopy. An immunohistochemical study was made with antibody anti-rabbit macrophages (RAM-11). Tensile strength was measured with an Instron tensiometer using 2-cm-wide strips obtained parallel to the shorter axis of the implant. DM induced little tissue adhesion to the material on the visceral peritoneum interface and was surrounded by organized repair tissue. The biomaterial was integrated in the repair tissue on the subcutaneous interface, but not on the peritoneal interface. The macrophage response decreased between days 14 and 90 (P < 0.001). Tensile strength increased significantly (P < 0.05) at every study period. We conclude that the DM prosthesis has little tendency to formation of visceral adhesions, the DM prosthesis was well tolerated by the receptor organism and the tensile strength of the prosthesis/receptor tissue interface increased with time.